1. Field of the Invention
The present invention relates to transmissions, and more particularly to tractor transmissions having different speed ranges including direct and underdrive coupling, and connections for power takeoff and front wheel drives.
2. History of the Prior Art
Transmissions for tractors and similar agricultural vehicles are desirably provided with a substantial variety of different speeds and speed ranges to accommodate the varying conditions under which such vehicles must operate. To be both versatile and efficient, tractors must be capable of operating at a wide range of speeds to accommodate a variety of different agricultural operations while at the same time being able to select a speed within a small, critical range for a given operation or set of conditions so as to be able to operate efficiently.
An example of a tractor transmission is provided by U.S. Pat. 3,774,474 of Recker et al, issued Nov. 27, 1973 and commonly assigned with the present application. The transmission described in the Recker et al patent provides for sixteen different speeds or gear ratios through use of a planetary section coupled between the engine and input shaft, a second clutch-operated section coupling the input shaft to a counter shaft and capable of being shifted between high and low speed ranges and a third section coupled between the counter shaft and an output shaft. The third section utilizes two different clutches in conjunction with four sets of gearing to provide a basic set of four speeds. The second section combines with the four speed third section to provide eight different speeds, with the eight speeds being extended to sixteen by the planetary section which can be shifted between direct drive and underdrive conditions.
Other examples of tractor transmissions are provided by U.S. Pats. No. 3,682,019 of Hoyer et al, No. 3,106,273 of Doerfer et al, No. 3,149,498 of Mack, No. 2,998,732 of Nelson, No. 2,747,416 of Swenson et al, No. 2,871,726 of Kamlukin, No. 2,880,833 of Stevenson et al, No. 2,982,153 of Albertson et al, No. 3,065,643 of Mark et al, No. 3,589,483 of Smith, No. 3,251,243 of Kress and No. 3,274,858 of Meyer et al.
Tractor transmissions of the type shown by the above-identified patents are typically provided with various driving connections in addition to the basic driving connection to the rear wheels of the tractor. Such additional connections may include a power takeoff connection and a mechanical front wheel drive connection. The power takeoff connection typically includes a power takeoff shaft which may be coupled to drive various agricultural implements and which is driven from the main part of the transmission through appropriate gearing and a clutch which controls coupling of the power takeoff shaft to the transmission. The mechanical front wheel drive connection also couples the main part of the transmission through appropriate gearing and a connect-disconnect clutch to a front wheel drive shaft. The front wheel drive shaft couples to the front wheels of the tractor through an appropriate axle and universal joint coupling.
Presently known tractor transmissions suffer from a number of limitations which may impair their efficiency in general and their usefulness for certain applications. One such problem arises from the difficulty in providing synchronized shifting between the different gears, particularly in arrangements where the components are to be compactly and efficiently arranged. The inability to shift smoothly and synchronously between different closely spaced speeds as load conditions change may require at the very least double clutching or at the extreme that the tractor be brought to rest before the gears can be changed. Another serious problem stems from the fact that clutches in the planetary section as well as in the front wheel drive sections are typically hydraulically operated. A potentially damaging situation exists when hydraulic pressure is reduced due to leakage or malfunction or completely lost in cases such as where the engine stalls or cannot be started. If the tractor is stalled or stopped with the planetary section in the high or direct drive condition in which the rotatable carrier housing the planetary gears is coupled to the input shaft from the engine, it may be impossible to tow start the tractor without running the risk of serious damage to the transmission. The loss of hydraulic fluid pressure may allow the planetary carrier to remain coupled to the input shaft so as to rotate at extremely high speeds with the resultant danger to or destruction of the bearings therefor when the tractor is towed. Stoppage of the tractor with the two clutches of the planetary section in a plurality engaged condition may also result in damage or destruction of the frictional components of the clutches.
Further dangers exist in connection with the front wheel drive connections in the event of loss of hydraulic fluid pressure such as where the tractor engine stalls. For example, if the tractor is being backed up a hill with the clutch of the front wheel drive connection engaged to provide primary driving from the front wheels, and the engine suddenly stalls, the sudden loss of hydraulic pressure may result in partial or complete disengagement of the front wheel drive clutch and consequent reliance solely on the rear wheels to try to control the tractor as it quickly begins to slide back down the hill.
Accordingly, it is an object of the invention to provide a multirange transmission capable of synchronously shifting between a plurality of closely spaced speeds within each range using an arrangement of components which is relatively simple and efficient.
It is a further object of the invention to provide a transmission in which a planetary section automatically shifts into the low or underdrive condition with loss of hydraulic pressure.
It is a still further object of the invention to provide a transmission in which the mechanical front wheel drive engages upon loss of hydraulic fluid pressure.